This Cubchoo is an ice-type Pokémon owned by Chris.
Chris tended to Cubchoo and played with it every day and locked it in a room beside the mansion. A Larvitar saw all that and unlocked the room to play with Cubchoo into a forest for a while. The heroes managed to find both of them playing and saw them happy with each other. After Chris had his first battle, using Larvitar against Ash's Scraggy, this inspired Cubchoo to become stronger as well.
None of Cubchoo's moves are known.